Urinary tract

Chapter 5 Urinary tract

Methods of imaging the urinary tract

1. Plain films
2. Excretion urography
3. Ultrasound (US)
4. Computed tomography (CT) – CT KUB, CT urography, ‘staging CT’, CT angiography
5. Magnetic resonance imaging (MRI) – MR urography, MR prostate, MR bladder, MR angiography
6. Micturating cystourethrography
7. Ascending urethrography
8. Retrograde pyeloureterography
9. Percutaneous renal puncture – nephrostomy, biopsy, antegrade pyelography, cyst puncture
10. Arteriography
11. Venography – including renal vein sampling
12. Conduitogram
13. Radionuclide imaging:
a Static
b Dynamic
c Radionuclide cystography – direct and indirect.

Further reading

Akin O., Hricak H. Imaging of prostate cancer. Radiol. Clin. North Am.. 2007;45(1):207-222.

Zhang J., Gerst S., Lefkowitz R.A., et al. Imaging of bladder cancer. Radiol. Clin. North Am.. 2007;45(1):183-205.

Zhang J., Lefkowitz R.A., Bach A. Imaging of kidney cancer. Radiol. Clin. North Am.. 2007;45(1):119-147.

Excretion Urography

Also known as intravenous urography (IVU). The technique is much less frequently used than in the past, being largely replaced by CT, MRI or US.

Indications

1. Haematuria
2. Renal colic
3. Recurrent urinary tract infection
4. Suspected urinary tract pathology.

Contraindications

See Chapter 2 – general contraindications to intravenous (i.v.) water-soluble contrast media and ionizing radiation. Pre-medication with steroids (see Chapter 2) may be considered but information regarding the renal size, presence of calcification and pelvicalyceal systems may be gained by using a combination of plain film, US, unenhanced CT and MRI.

Contrast medium

Low osmolar contrast material (LOCM) 370

Adult dose

50–100 ml

Paediatric dose

1 ml kg−1

Patient preparation

1. No food for 5 h prior to the examination. Dehydration is not necessary and does not improve image quality.
2. Patients should, preferably, be ambulant for 2 h prior to the examination to reduce bowel gas.
3. The routine administration of bowel preparation fails to improve the diagnostic quality of the examination and its use makes the examination more unpleasant for the patient.

Preliminary film

1. Supine, full-length anterior posterior (AP) of the abdomen, in inspiration. The lower border of the cassette is at the level of the symphysis pubis and the X-ray beam is centred in the mid-line at the level of the iliac crests.

If necessary, the position of overlying opacities may be further determined by:

a supine AP of the renal areas, in expiration. The X-ray beam is centred in the mid-line at the level of the lower costal margin

or

b 35° posterior oblique views

or

c tomography of the kidneys at the level of a third of the AP diameter of the patient (approx. 8–11 cm). The optimal angle of swing is 25–40°.

The examination should not proceed further until these films have been reviewed by the radiologist and deemed satisfactory.

Technique

Venous access via the median antecubital vein is the preferred injection site because flow is retarded in the cephalic vein as it pierces the clavipectoral fascia. The gauge of the cannula/needle should allow the injection to be given rapidly as a bolus to maximize the density of the nephrogram.

Upper arm or shoulder pain may be due to stasis of contrast medium in the vein. This is relieved by abduction of the arm.

Films

1. Immediate film. AP of the renal areas. This film is exposed 10–14 s after the injection (approximate arm-to-kidney time). It aims to show the nephrogram, i.e. the renal parenchyma opacified by contrast medium in the renal tubules.
2. 5-min film. AP of the renal areas. This film is taken to determine if excretion is symmetrical and is invaluable for assessing the need to modify technique, e.g. a further injection of contrast medium if there has been poor initial opacification.

A compression band is now applied around the patient’s abdomen and the balloon positioned midway between the anterior superior iliac spines, i.e. precisely over the ureters as they cross the pelvic brim. The aim is to produce better pelvicalyceal distension. Compression is contraindicated:

a after recent abdominal surgery
b after renal trauma
c if there is a large abdominal mass or aortic aneurysm
d when the 5-min film shows already distended calyces.
3. 10-min film. AP of the renal areas. There is usually adequate distension of the pelvicalyceal systems with opaque urine by this time. Tomography may be useful to improve visualization of the pelvicalyceal systems if these are obscured by bowel.
Compression is released when satisfactory demonstration of the pelvicalyceal system has been achieved.
4. Release film. Supine AP abdomen. This film is taken to show the whole urinary tract. If this film is satisfactory, the patient is asked to empty their bladder.
5. After micturition film. Based on the clinical findings and the radiological findings on the earlier films, this will be either a full-length abdominal film or a coned view of the bladder with the tube angled 15° caudad and centred 5 cm above the symphysis pubis. The aims of this film are to assess bladder emptying, to demonstrate a return to normal of dilated upper tracts with relief of bladder pressure, to aid the diagnosis of bladder tumours, to confirm ureterovesical junction calculi and, uncommonly, to demonstrate a urethral diverticulum in females.

Additional films

1. 35° posterior obliques of the kidneys, ureters or bladder
2. Tomography – when there are confusing overlying shadows
3. 30° caudad angulation of the tube for the renal area. This may throw a faecal laden transverse colon clear of the kidneys
4. Prone abdomen – may improve visualization of ureters by making them more dependent
5. Delayed films – may be necessary for up to 24 h after injection in obstructive uropathy.

ULTRASOUND OF THE URINARY TRACT IN ADULTS

Indications

1. Suspected renal mass lesion
2. Suspected renal parenchymal disease
3. Possible renal obstruction
4. Haematuria
5. Hypertension resistant to conventional medical treatment
6. Renal cystic disease
7. Renal size measurement
8. To facilitate accurate needle placement in interventional procedures
9. Prostatism
10. Bladder volume before and after micturition
11. Bladder tumour
12. Following renal transplant to assess the pelvicalyceal system and patency of vessels, and to investigate perirenal collections.

Contraindications

None.

Patient preparation

None – unless full bladder is required.

Equipment

3.5–5 MHz transducer. Contact gel. The choice of pre-set protocol and positioning of focal zones will depend upon the type of US machine.

Technique

1. Patient supine, right (RAO) and left anterior oblique (LAO) positions or prone for kidneys. The kidneys are scanned longitudinally and transversely. The right kidney may be scanned through the liver and posteriorly in the right loin. The left kidney is harder to visualize anteriorly unless the spleen is large, but can be visualized from the left loin.
2. The length of the kidney measured by US is smaller than that measured at excretion urography because there is no geometric magnification and no change in size related to contrast-induced osmotic diuresis. With US measurement, care must be taken to ensure that the true longitudinal diameter is scanned. The mean length of the normal adult right kidney is 10.7 cm and the left 11.1 cm (range 9–12 cm).
3. The bladder is scanned suprapubically in transverse and longitudinal planes. Measurements taken of three diameters before and after micturition enable an approximate volume to be calculated.
4. Colour flow and duplex Doppler may be used to examine the renal arteries and veins.
5. Renal transplants are usually located in the right or left iliac fossa. These usually lie fairly superficially. Attention should be paid to the pelvicalyceal system and renal vessels.

ULTRASOUND OF THE URINARY TRACT IN CHILDREN

The availability of high-resolution real-time US has revolutionized the investigation of paediatric renal disease. It demonstrates anatomy without the necessity for adequate renal function but, because it gives no functional information, it is the ideal complement to nuclear medicine imaging. It should be stressed that the technique is only as good as the effort put in to obtain the images.

Indications (after Lebowitz, 1985)1

1. Urinary tract infection – to document scarring, elicit signs of acute upper tract infection and to exclude an underlying structural abnormality.
2. An abdominal or pelvic mass. Ultrasonography will demonstrate the relationship of the mass to other organs, its possible site of origin and its characteristics, i.e. solid or cystic and the presence of calcification.
3. Renal failure – to differentiate medical from surgical causes.
4. Abnormal antenatal US – to confirm or refute an antenatal diagnosis of hydronephrosis or multicystic dysplasia. The role of US should be to help in the efficient planning of the postnatal management before infection occurs and plasma creatinine rises, rather than to provoke antenatal intervention. It must be remembered that, because urine output falls rapidly after birth when compared with in utero, US on day 1 may show considerably less pelvicalyceal dilatation than was observed on the antenatal scans. Further follow-up scans are mandatory.
5. Conditions associated with a high likelihood of renal abnormalities, e.g. imperforate anus and genital anomalies. The most frequently found abnormalities are a single or ectopic kidney.
6. Genetic conditions, such as Beckwith–Wiedemann, which predispose to >5% risk of developing Wilms’ tumour.2 US surveillance should be performed every 3–4 months.
7. Screening of family members for genetically linked renal diseases, e.g. dominant polycystic renal disease.
8. Periodic follow-up of kidneys which are at risk of deterioration, e.g. children with myelomeningocele or urinary diversion. Patients on chronic dialysis have a high incidence of acquired cystic disease and may develop adenomas or adenocarcinomas.
9. To assess the patency of the IVC and renal vein in patients with Wilms’ tumour.
10. To assess residual bladder volume.
11. To facilitate the accurate placement of needles for renal biopsy, antegrade pyelography, percutaneous nephrostomy, cyst aspiration and drainage of perinephric collections.

When assessing possible renal disease by ultrasonography, a number of normal ‘variants’ may be confused with disease. These include increased parenchymal echogenicity in the neonatal period, echo-poor papillae which may mimic dilated calyces and persistent fetal lobulation, hepatic and splenic impressions, and parenchymal junctional lines, which may mimic scarring.

Equipment

3.5–7.5 MHz transducer – dependent on age.

Patient preparation

Full bladder. Patients with an indwelling catheter should have this clamped 1 h before the examination is scheduled.

Technique

1. Begin by examining the bladder, because contact of the transducer and jelly against the skin may promote bladder emptying. You may have only one chance to image the bladder.
2. It may be necessary to examine uncooperative children while they sit on a carer’s lap. Otherwise the technique is as for adults.
3. If possible the kidneys are examined in full inspiration or with the child being asked to ‘push the tummy out’.

References

1 Lebowitz R.L. Pediatric uroradiology. Pediatr. Clin. North Am.. 1985;32:1353-1362.

2 Scott R.H., Walker L., Olsen Ø.E., et al. Surveillance for Wilms tumour in at-risk children: pragmatic recommendations for best practice. Arch. Dis. Child.. 2006;91:995-999.

Computed Tomography of the Urinary Tract

Indications

1. Renal colic/suspected renal stone disease
2. Suspected renal tumour
3. Suspected renal/perirenal collection
4. Loin mass
5. Staging and follow-up of renal, transitional cell or prostatic cancer. Local staging of prostatic cancer is performed using high-resolution MRI or endorectal US. Local staging of bladder cancer may be performed using MRI or CT
6. Investigation of obstructive uropathy
7. CT angiography may be used to assess renal vessels for suspected renal artery stenosis or arterio-venous fistula or malformation.

Technique

Computed tomography of kidneys, ureters and bladder

CT KUB (non-contrast enhanced CT of kidneys, ureters and bladder) is useful to determine the number and location of urinary tract calculi. It is used in some centres as the primary investigation of renal colic:

1. The patient lies in prone position on CT scanner table.
2. A scout view is obtained.
3. A low-radiation-dose technique is used to scan from the top of the kidneys to include the bladder base with a slice thickness of 5 mm or less, as determined by CT scanner. An i.v. contrast is not given.

CT urogram

This technique uses a combination of unenhanced, nephrographic and delayed scans following i.v. contrast to allow examination of renal parenchyma and collecting systems. This is one suggested method:

1. Venous access is obtained
2. Patient lies in supine position
3. Scanogram is obtained
4. Initial low-dose unenhanced scans of urinary tract if renal stone disease is suspected
5. Low osmolar contrast material (LOCM) 300 (100–150 ml) is given as bolus intravenously
6. 3 mm or less thickness scans are obtained from diaphragm to lower poles of kidneys during nephrographic/parenchymal enhancement phase (100–120 s following start of bolus injection)
7. If possible, the patient is then encouraged to walk freely within the scan room or department for a few minutes
8. 3 mm or less thickness scans are obtained from upper pole of kidneys to bladder base 10 min after contrast injection, to examine collecting systems and ureters
9. Reconstructions can then be made of the pelvi-calyceal systems and ureters in appropriate planes.

‘Staging CT’

This technique is used to stage and follow-up known renal-tract malignancy or to investigate more non-specific signs attributed to the renal tract. Examination of the thorax in addition to the abdomen and pelvis is often appropriate in conditions where pulmonary metastatic disease or mediastinal nodal spread is a possibility:

1. Venous access is obtained
2. Patient lies supine on the scanner
3. Scanogram of chest, abdomen and pelvis as appropriate
4. 100 ml i.v. LOCM given
5. Scans obtained approximately 70 s after i.v. contrast at 5 mm slice thickness or less, depending upon scanner. Arterial phase scans of the liver (20–25 s after i.v. contrast) may be appropriate in those patients with suspected metastatic renal cancer who may have hypervascular liver metastases.

CT angiography

Indications

1. Renal artery stenosis
2. Renal artery aneurysm, arteriovenous malformation, dissection or thrombosis
3. Delineation of vascular anatomy prior to laparoscopic surgery, e.g. nephrectomy
4. Renal vein thrombosis or renal vein/IVC tumour.

Technique

1. No oral iodinated contrast used.
2. Localize the renal hilum accurately using non-enhanced images.
3. Use narrow collimation (1–3 mm).
4. 100–150 ml i.v. contrast medium (LOCM 300) injected at 3–4 ml s−1.
5. Use of bolus triggering devices is recommended to ensure appropriate timing. Otherwise scans are initiated after a preset empiric delay of 20–25 s from start of contrast material injection.
6. Examination of the inferior vena cava requires scanning at a later time (90–120 s delay).

Further reading

Kluner C., Hein P.A., Gralla O., et al. Does ultra-low-dose CT with a radiation dose equivalent to that of KUB suffice to detect renal and ureteral calculi? J. Comput. Assist. Tomogr.. 2006;30(1):44-50.

Van Der Molen A.J., Cowan N.C., Mueller-Lisse U.G., et alCT Urography Working Group of the European Society of Urogenital Radiology (ESUR). CT urography: definition, indications and techniques. A guideline for clinical practice. Eur. Radiol.. 2008;18(1):4-17.

Magnetic Resonance Imaging of the Urinary Tract

Indications

1. Local staging of prostatic cancer
2. Local staging of bladder cancer
3. Staging of pelvic lymph nodes
4. Suspected renal mass
5. Screening of patients with von Hippel–Lindau disease or their relatives
6. Suspected renal obstruction in patients with poor renal function
7. MR angiography: of potential living related donors, suspected renal artery stenosis.

Technique

Technique will be tailored to the clinical question with MR urography used to investigate the renal tract as a whole. MRI of the abdomen and pelvis can be obtained to assess retroperitoneal adenopathy as part of the staging investigations for patients with bladder and prostate cancer, but CT is often used for this purpose with MRI used for local staging.

MAGNETIC RESONANCE UROGRAPHY

The two most common MR urographic techniques are:

1. static (fluid-filled) urography using heavily T2-weighted MRI techniques to display fluid-filled structures in a similar fashion to magnetic resonance cholangiopancreatography (MRCP) (see Chapter 4)
2. excretory MR urography using T1-weighted gadolinium enhanced scans.

In and out of phase T1-weighted gradient echo scans can be performed to characterize adrenal mass lesions or identify lipid within angiomyolipomas and clear cell carcinoma of the kidney.

Indications

1. To demonstrate the collecting system/determine level of obstruction in a poorly functioning/obstructed kidney
2. Urinary tract obstruction unrelated to urolithiasis. Suspected renal colic from calculus is probably better imaged with CT KUB/ IVU
3. Congenital anomalies
4. Potential renal transplant donors (combined with MR angiography and standard MR imaging of renal parenchyma).

Technique

1. The patient is supine with an empty bladder.
2. Scout views are obtained.
3. Static MR urography may be performed prior to excretory urography.

Thick-slab, single-shot, fast-spin echo or a similar thin-section technique, e.g. half-Fourier rapid acquisition with relaxation enhancement; single-shot, fast-spin echo; single-shot, turbo-spin echo. Three-dimensional respiratory triggered sequences may be used to obtain thin-section data sets that may be further manipulated.

The use of hydration, compression or diuretics may be used to improve visualization of non-dilated collecting systems.

4. Diuretic administration (e.g. 5–10 mg furosemide for adults) given prior to i.v. contrast, can improve the distension of the collecting system and dilute the contrast within the collecting system improving the quality. This may be omitted in patients shown to have obstruction on static MR urography.
5. Excretory MR urography uses pre- and post-contrast scans in the same position. A gadolinium-based contrast agent is administered i.v. using a dose of 0.1 mmol gadolinium/kg body weight. The collecting systems are imaged during the excretory phase using a breath-hold, three-dimensional gradient echo, T1-weighted sequence. Nephrographic phase images may be obtained to image renal parenchyma. Fat suppression will improve the conspicuity of the ureters. Sequences, such as VIBE (volumetric interpolated breath-hold examination) or LAVA (liver acquisition with volume acceleration) can be used. T2* effects from a sufficient concentration of contrast agent may reduce the signal intensity of urine and potentially obscure small masses within the collecting system. This can be overcome, to a certain extent, by using lower concentration of i.v. contrast (e.g. 0.01 mmol kg) but this technique will not distend the collecting system and may compromise soft-tissue imaging. The optimum concentration of contrast has not been established as yet.

Further reading

Leyendecker J.R., Barnes C.E., Zagoria R.J. MR urography: techniques and clinical applications. Radiographics. 2008;28(1):23-46. discussion 4647

Nikken J.J., Krestin G.P. MRI of the kidney – state of the art. Eur. Radiol.. 2007;17(11):2780-2793.

Takahashi N., Kawashima A., Glockner J.F., et al. Small (<2-cm) upper-tract urothelial carcinoma: evaluation with gadolinium-enhanced three-dimensional spoiled gradient-recalled echo MR urography. Radiology. 2008;247(2):451-457.

Magnetic Resonance Imaging of the Prostate

Technique

1. Patient supine

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Feb 20, 2016 | Posted by in GENERAL RADIOLOGY | Comments Off on Urinary tract

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